1906.] The Pharmacology of Ethyl Chloride. 409 



may, in some instances' in which there is exalted vagus irritability, stop 

 before the respiration. 



Conclusions. — In ethyl chloride narcosis the integrity of the respiratory 

 mechanism is dependent upon the maintenance of blood-pressure. 



Paralysis of respiration may be preceded by shallow respiratory movements, 

 but it is usually preceded by deep and delayed breaths, and in some cases 

 the prolonged pause between the expiration and the following inspiration 

 prevents the fall of blood-pressure. 



In all of the experiments performed the respiration failed before the 

 heart. 



Conclusions. 



Conclusions with Regard to the Effects of Ethyl Chloride on Dogs. 



(1) Quantities above 9 per cent, of ethyl chloride in the air respired exert 

 a paralytic effect upon heart muscle similar to that produced by chloroform 

 in y'g-th the concentration. 



(2) The central vaso-motor system is at first stimulated, and the peripheral 

 mechanism of the arterioles is paralysed. The local paralytic effect is 

 more significant than the central stimulation, so that the sum of these 

 opposing factors is relaxation. This result is similar to that produced by 

 chloroform, but the effect is never so profound, and requires for its production 

 much higher concentration of ethyl chloride vapour. 



(3) Its effect upon the vagus system is one of stimulation, and with high 

 concentration the heart is readily arrested by vagus inhibition. As, however, 

 the spontaneous excitability of the heart muscle is not seriously impaired, 

 the heart escapes from vagus inhibition, and in no case has death occurred 

 from this cause. To produce the same inhibitory effect with chloroform 

 requires approximately a quarter the concentration in the respired air. 

 Since it requires xgth the concentration of chloroform to produce the same 

 paralytic effect upon heart muscle, inhibition from ethyl chloride must 

 ensue a variable period before the spontaneous excitability of the heart muscle 

 is seriously impaired. 



It is on this difference between the action of the two anaesthetics that the 

 relative safety of ethyl chloride rests. The vagus system is not so readily 

 depressed by prolonged administration as is the case with chloroform. 



(4) Like chloroform the respiration under ethyl chloride narcosis is 

 dependent upon the maintenance of the blood-pressure. The cause 

 of the fall of blood-pressure from ethyl chloride is mainly vagus inhibition, 

 whereas that from chloroform is cardiac paralysis completed by inhibition. 

 Eespiratory failure occurring apart from fall of blood-pressure, as, for 



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